The present invention relates to cutting blades, such as saw blades, and processes of producing such blades, and is more particularly directed to improvements in blades with self-sharpening cutting edges.
Cutting and saw blades are used in a variety of household and industrial applications, including razors, knives, shears, agricultural implements, rotary cutters and slicers, chisels, power saws, band saws, and hand held hack saws.
Users desire cutting blades with sharp edges possessing long life and corrosion resistance. Typically, blades are initially sharpened to form a wedge shaped cutting edge and re-sharpened as needed, except in the case of razor blades which cannot be re-sharpened.
Sharpness of a cutting blade is measured in terms of xe2x80x9cultimate tip radiusxe2x80x9d, which is different depending on the application. For kitchen knives, rotary cutters, and similar cutting instruments, ultimate tip radius may be several thousand Angstroms. In agricultural implements incorporating rotary blades that cut through the soil, axes, and in chisels, the cutting edge radius may be expressed in microns or even in millimeters rather than Angstroms. Shaving razor blades ordinarily have ultimate tip radii of about 1,500 Angstroms or less. This radius usually includes a layer of hard material coating applied to the wedge shaped base material of the razor blade.
Among cutting blades, razor blades incorporate the most stringent technological requirements. Typically, a base material (usually a martensitic stainless steel strip) is ground and honed on one edge to a wedge shape with an included angle of 30 degrees or less, coated with a 200-900 Angstrom thick layer of hard material for improved life, and coated with up to 10 xcexcm thick layer of low friction coefficient organosiloxane gel, or a fluorocarbon polymer.
Many variations of the contemporary razor blade technology have been proposed. Polycrystalline ceramics were proposed as the base material by Kramer (U.S. Pat. Nos. 5,056,227 and 5,142,785) and by Hahn (U.S. Pat. No. 5,048,191). A totally glass razor was the subject of U.S. Pat. No. 4,702,004 to Haythornthwaite, and a compaction of hollow fibers was offered by Siegmund and Strack in their U.S. Pat. No. 3,805,387. As hard coatings, boron carbide (U.S. Pat. No. 5,129,289 by Boland et al.), diamond, and diamond-like carbon (DLC) coatings were offered in U.S. Pat. No. 5,142,785 by Kramer. Methods of application of fluorinated polymer films can be found in U.S. Pat. No. 5,088,202 to Boland et al., and in U.S. Pat. No. 4,330,576 to Dodd.
Like blades for knives and rotary cutters, razor blades are sharpened to ideal wedge angles and cutting tip radii in order to perform satisfactorily. Unfortunately, as soon as these blades are subjected to wear conditions in service, they begin to loose their sharpness. In other words, their ultimate performance can only occur at the beginning of their service life and their performance will continually diminish with time. This happens by loss of material from the blade tip which leads to increase of tip radius.
In most cases, cutting blades become dull by gradual loss of material due to wear of cutting edges. Wear mechanisms may include general and grain boundary corrosion, as well as chipping and loss of grains due to weak grain boundaries. In general, the harder the material, the more resistant it is to wear. However, if grain boundary weakness and loss of grains are part of the wear mechanism, hardness alone may not be the most important factor determining wear resistance.
Saw blades may be made of a single metallic material, or may have teeth with welded or bonded carbide tips. Initial sharpness of saw blades diminish with time and the blades must either be thrown away or re-sharpened. When a carbide tip wears, it must be reapplied, which consumes valuable time.
This invention provides a solution to the problem of blade edge dulling by providing self-sharpening blades with layered structures where the thickness of the most wear resistant layer determines the sharpness of the blade, and as the blade wears in service, cutting tip diameter, and therefore the blade sharpness, remains unchanged. Saw blades provided by this invention are similarly self-sharpening type blades.
It is an object of this invention to provide self-sharpening cutting blades of the types used in shaving razors, kitchen knives, industrial knives, shears, agricultural implements, earth and rock cutting tools, rotary cutters, rotary slicers, chisels, axes, and other similar cutting instruments.
It is another object of this invention to provide self-sharpening saw blades of the types used in power saws, hand-held hack saws, and other similar sawing instruments.
Another object is to provide a layered composite or laminate which comprises
a) a layered structure,
b) that structure including a relatively harder first layer with relatively higher wear resistance extending to a blade cutting edge,
c) the structure also including a second layer characterized by relatively lesser hardness and lesser wear resistance and located at one side of the first layer.
A further object is to provide a third layer also characterized by relatively lesser hardness and wear resistance than that of the first layer, the second and third layers located at opposite sides of the first layer.
The foregoing and other objects and advantages are in part attained by selection of various materials that make-up self-sharpening cutting blades and saw blades on the basis of their wear resistance. This invention provides a solution to the problem of blade edge dulling experienced in conventional cutting blades and saw blades by providing self-sharpening blades with layered structures where in the most wear resistant layer thickness determines the sharpness of the blades, and as the blade wears in service, cutting tip diameter, and therefore the blade sharpness, remains unchanged. Saw blades provided by this invention are similarly self-sharpening type blades.
In its simplest form, a self-sharpening cutting blade is created by placing a hard material layer of pre-selected thickness and high wear resistance at the center of the blade body and extending to the cutting edge, and within a matrix body material possessing lesser wear resistance. Relative difference in wear resistance of the higher wear resistant material at the central cutting tip of the blade, versus the relatively lower wear resistance of the rest of the blade, creates a self-sharpening effect in service. Because the softer, less wear resistant matrix material wears faster than the more wear resistant hard material layer located in the center of the blade""s cross-section, the hard material layer is always exposed at the very tip of the blade. Additionally, the hard material layer thickness is selected to be approximately equal to the xe2x80x9cultimate tip diameterxe2x80x9d, and is substantially the same everywhere within the hard layer. Thus, as the cutting edge of the blade wears in service, exposed hard material layer at the very tip of the cutting edge will always have the ideal xe2x80x9cultimate tip diameterxe2x80x9d, and provide the best performance in service.
Similar to cutting blades, in self-sharpening saw blades of this invention a hard material layer selected for its high wear resistance wears less than the matrix material when subjected to wear conditions in service. Because the hard material layer has a constant or uniform thickness optimally selected for a given application, its sharpness, and therefore the performance of the saw, is maintained throughout usage of the saw. Thus, the self-sharpening saws of this invention perform at their best and last considerably longer than conventional saw blades, which begin to dull immediately after first usage.
These and other objects and advantages of the invention, as well as the details of an illustrative embodiment, will be more fully understood from the following specification and drawings, in which: